Electrical steel sheets and strips having excellent punching and welding characteristics for the use of a laminated iron core

ABSTRACT

Electrical steel sheets and strips having excellent punching and welding characteristics for production of a laminated iron core, which comprises an organic type coating film applied on the surface of an electrical steel sheet and strip substrate having a surface roughness larger than 20 Hr.m.s. Mu inch.

United States Patent [191 Kltayama et al.

[ ELECTRICAL STEEL SHEETS AND STRIPS HAVING EXCELLENT PUNCHING ANDWELDING CHARACTERISTICS FOR THE USE OF A LAMINATED IRON CORE [75]Inventors: Minoru Kitayama; Montonaru Nakamura; Kiyoshi Matsui; HiroshiOkada, all of Himeji, Japan [73] Assignee: Nippon Steel Corporation,Tokyo,

Japan [22] Filed: Sept. 15, 1971 [21] Appl. No.: 180,653

[30] Foreign Application Priority Data Sept. 17, 1970 Japan 45-81473Dec. 7, 1970 Japan 45-108353 [52] U.S. Cl. 117/230, 148/315, 148/615 R,148/62, 117/49 [51] Int. Cl. C23f 7/10, C23f 7/26 Feb. 19, 1974 [58]Field of Search 117/230; 148/615, 31.5; 29/4723, 609

[56] References Cited UNITED STATES PATENTS 3,632,362 l/l972 Urashiyamaet al 117/230 X 2,904,875 9/l959 Trigg et al. ll7/230 X 3,291,63612/1966 Reighter et a]. ll7/230 X Primary Examiner-Ralph S. KendallAttorney, Agent, or Firm-Toren and McGeady [5 7] ABSTRACT Electricalsteel sheets and strips having excellent punching and weldingcharacteristics for production of a laminated iron core, which comprisesan organic type coating film applied on the surface of an electricalsteel sheet and strip substrate having a surface roughness larger than20 Hr.m.s. ,inch.

3 Claims, 10 Drawing Figures PATENTEB FEB 1 9 i974 SHEET 1 BF 5 'FIGJ 5m$502 tan 29m: 5:: mmc ucza *0 000 9 EnEz Amount of organic film indouble-layer film( /m) INVENTORS 9 ne "V M J m INN K 9 R U Day 00 mum"Nun VIRUS!!! 0136. 1 z ,7 l ATTORNEYS sum 2 or 5 FIG. 2 ((1) 0 O A A AEEGV numam 0522s PAIENTEB FEB I 91974 Mo HARD NA Haw R H) yosmPATENIEBFEM 9 1914 Welding speed N -l o 0 SHEET U 0F 5 Surface Roughnessof Film ,a H max 1N VENTORS M Nom) NITAYAMA MOTOHARU NAKAMURA sm MA'TBUIBY MMWW TORNEB PATENTEDFEB 3, 793 073 SHEET 5 BF 5 SURFACE ROUGHNESSSTEEL SHEET SMOOTH GRADE 40 Hr. m. 5; inch WELDING SPEED-'40crnfiwn.WELDING SPEED: 60 cm/ml'n.

F I G. 4 a FIG. 4 d

SURFACE aoueuuessmo HnmSpinch smoom GRADE WELDING speemaocmlmln. WELDING$PEED 60cm/min.

FIG. 4 b FIG. 4e

SURFACE nousuuessmonnmspinch SMOOTH GRADE WELDING spEEnuoocmfinin. wawmsSPEED! aocmlmm.

FIG. 4:: FIG. 4F

ELECTRICAL STEEL SHEETS AND STRIPS HAVING EXCELLENT PUNCHING AND WELDINGCHARACTERISTICS FOR THE USE OF A LAMINATED IRON CORE This inventionrelates to electrical steel sheets and strips for production of alaminated iron core, having excellent punching characteristics forobtaining iron cores and having excellent welding characteristics forwelding said punched steel sheets and strips into a laminated iron core.

To obtain an iron core for motors and transformers for use in domesticelectrical instruments, electrical steel sheets and strips are punchedcontinuously, piled and then their edges are welded.

In such a case, the polishing and changing of the punching die when theburr thereon becomes too high requires considerable time. Thus, it isrequired that the punching can be done as much as possible with a singlepolishing, namely, the punching characteristic of the steel sheet shouldbe excellent. To obtain a laminated iron core by welding the edges ofthe pile of punched steel sheets and strips, it is required at the sametime, in order to increase the working efficiency, that the welding canbe done with as fast a speed as possible under a certain electriccurrent and a certain screwing pressure without causing defects, suchas, blowholes, at the welded part. Then, the welding characteristicsshould also be excellent.

While the punching characteristics depends on the quality of theelectric steel sheet and strip, the insulating film applied on thesurface thereof also has a remarkable influence. An inorganic coatingfilm, for instance, of the phosphoric acid type, chromic acid type or acombination thereof has hitherto been used for such an insulating film.However, without considering the welding characteristics, only 50,000150,000 punchings can be made by such treatment until the height of theburr on a steel dye reaches 50.

In order to improve the punching characteristic, an organic coating filmhas been utilized in recent years. The punching characteristic isimproved remarkably by such a procedure. 1,000,000 3,000,000 punchingscan be made until the height of the burr reaches 50 in punching with thea steel die, which corresponds to the punching characteristic obtainedwith the use of a super hard die in the case of a non-organic type film.As a result, the economical effect is remarkable, shortening both thetime required for exchanging the die in the punching as well as the timefor polishing the die. On the other hand, however, the organic film isdecomposed by the heat of welding in the welding of the pile of punchedsteel sheets and strips in the subsequent stage and gives off a volatilegas. The gas permeates into the welding bead and spout out as bubblesfrom the head. This forms blowholes in the welded part and causesserious problem in the welding operation.

An example of the relationship between the quantity of the organic filmand the punching and welding characteristics in the double layer coatingtreatment will be shown graphically in FIG. 1.

Coating condition Under layer: zinc bichromate type, amount of filml.5g/m

Upper layer: varying amounts of the film comprising a mixture ofpolyvinyl formal, phenol resin and melamine resin Testing conditionPunching: steel die, clearance 5 percent, light oil as a punching oilWelding: electric current 120 A, screwing pressure l00kg/cm weldingspeed 20cm/min. and 60cm/min.

Judgement of welding characteristics @2 no blowhole 0: some blowholes A:blowholes are formed on a half of beads x: blowholes are formed entirelyon beads As it is obvious from FIG. 1, a quite excellent punchingcharacteristic with more than 1,500,000 punchings until the height ofburr reaches p can be obtained when the amount of the upper (organic)coating film is more than l.5g/m On the contrary, however, regarding thewelding characteristic after piling the punched steel sheets and strips,in welding under the standard condition, i.e., an electric current of120 A and the welding speed of cm/min., while the steel sheets andstrips with an upper layer film of 0.25g/m may be usable although theformation of some blowholes is observed, the sheet with an upper film ofmore than 0.25g/m can not be used as the formation of blowholes isenormous. When the welding speed is lowered to 20cm/min., the sheet withan upper film of up to lg/m can be used. However, consideringthe safetyfactors, the consumer is obliged to use a welding condition with aremarkably low efficiency, such as, a welding speed of 5 15cm/min.

As above-mentioned, there is an incompatible relationship between thepunching characteristic and the welding characteristic of the pile ofpunched steel sheets and strips in the case of an organic type coatingfilm. It has been eagerly desired for a long while to obtain a laminatediron core having excellent characteristics in punching as well as inwelding of the pile of punched steel sheets and strips.

Thus, the present inventors intended to offer electrical steel sheetsand strips suitable for production of a laminated iron core having bothof the characteristics above-mentioned, and have succeeded in developingelectrical steel sheets and strips with organic coating films on theirsurface having both characteristics which give excellent welding resultsin the welding of a pile of punched steel sheets and strips.

Namely, the present invention relates to electrical steel sheets andstrips having excellent punching and welding characteristics in whichthe surface of the steel sheets and strips is made rougher than that ofcommon steel sheets and strips; namely the surface is made rougher than20 Hr.m.s.p. inch, and a coating film comprising various kinds oforganic material as mentioned hereinafter is applied thereon.

The present inventors have considered that the formation of blowholes inthe welding of a laminated iron core is due to the phenomena that thevolatile gas evolving from the organic coating film by the heat ofwelding permeates into the welding beads before the beads solidify, andthe gas thus occluded stays therein or spouts out as bubbles. Thus, thepresent inventors tried to give a proper roughness to the surface of thesteel sheets and strips intentionally in order to make a gap to permitthe gas to pass. therethrough, thus 'enabling easy removal of thevolatile gas evolving from the coating film from the surroundings of thewelded part when the organic coating film is decomposed in the course ofthe welding of the pile of punched steel sheets and strips. As a result,quite expectedly, a welded part having no blowhole is obtainedsuccessfully.

The roughness of the surface of conventional electrical steel sheets andstrips with an insulating film (socalled smooth grade) has usually been5 l5 Hr.m.s.p. inch. The prior art gives no information on the effect ofimproving the welding characteristic after piling steel sheets andstrips by regulation of the roughness of the surface of the steelsheets. Moreover, in applying an inorganic type insulating film, nosteel sheets and strips whose surface is rougher than above-mentionedhave ever been adopted because the insulating and anticorrosivecharacteristics are inferior.

As a result of investigations on the relation between the weldingcharacteristic and the roughness of the surface of steel sheets andstrips when the pile of punched steel sheets and strips having anorganic coating film is welded, the present inventors have found that,as shown in FIG. 2(a), with an identical composition of steel, coatingfilm and coating amount, no formationof blowholes was observed. Even ina high speed welding process when the roughness of the steel surface wasgreater than 20 Hr.m.s.p. inch, and particularly with the use of aroughness of greater than 25 Hr.m.s.;t inch, no formation of blowholeswas observed at all even when an astonishingly high welding velocity ofIOOcm/min. far beyond the commonly considered standard velocity of60cm/min. was applied.

While there are various methods for determining the surface roughness byusing an apparatus, such as, the contact needle type surface roughnessmeasuring apparatus, the light cutting apparatus and the lightinterference type voidmeter, the contact needle type profilometer madeof the Bendix (Type LK Tracer) was used in the present invention.

The welding characteristics of the steel sheets and strips having adouble layer coating film with inorganic and organic materials is shownin FIG. 2(b). Similarly to the result in FIG. 2(a), the steel stripswith the surface roughness of greater than about 20 Hr.m.s.p. inch alsohave an excellent welding characteristic. The same is also true for thesingle layer coating film comprising a mixture of inorganic and organicmaterials. The reason may be considered as due either to the formationof sufficient passage for the volatile gas evolved by the decompositionof the organic coating' film due to the heat of welding in theneighbourhood of the welded part by making the steel surface adequatelyrough,'or to the previous existence of sufficient pass way for thevolatile gas to escape during welding due to'the roughness of thesurface of the organic coating film, which may be formed by theinfluence of the surface roughness of the steel strips.

Another feature of this invention concerns electrical steel sheets andstrips having excellent punching and welding characteristics in whichthe surface of an organic coating film itself applied on the surface ofsteel sheets and strips is made rougher than in the case of commonorganic coating film.

As a result, a welded part having no blowholes can be obtainedsuccessfully, and the welding speed can be astonishingly increased.

The surface of organic coating film applied on the surface of electricalsteel sheet and strip has hitherto been very smooth, i.e., less than ld-[ (l dz hR.m.s.p.inch). FIG. 3 shows the relationship between thesurface roughness of the organic coating film applied and the weldingcharacteristic in a double layer coating comprising inorganic andorganic coating films. 5 As it is obvious from this example, the effectof improving the welding characteristic is obtained when the surfaceroughness of the organic coating film is greater than ZpH The reason maybedue to the fact that the volatile gas evolved during welding is easilyre moved from the surroundings of the welded part. It has been provedthat, in increasing the surface roughness greater than Z H no formationof blowholes takes place at all even when an astonishingly high weldingvelocity of IOOcm/min. far beyond the commonly considered standardvelocity of 60cm/min. is adopted.

Similar results were also obtained in the cases of one layer organiccoatings and a one layer coating with a mixture of inorganic and organicmaterials.

Although said surface roughness of the steel sheet and strips,Hr.m.s.p.inch, as well as the surface rough-ness of the coating film,ZpJ-I deviate somewhat according to the method and condition ofdetermination, it goes without saying that the range of such a deviationbelongs naturally to the scope of this invention so long as the objectof the invention is attained. While the welding characteristic improveswith increasing the surface roughness of the steel sheet and strips aswell as the coating film, as there is a tendency to decrease the rate ofoccupied area, this relation should be considered in the embodiment.

As the insulating film of this invention is of'an organic type, thesurface tension is small, the wetting and adhesive characteristics areexcellent, and moreover, the corrosion resistance of the coating filmitself is also superior. Therefore, a satisfactory result in theinsulating and anticorrosive characteristics can be obtained even whenthe steel surface is fairly rough.

As the welding characteristic is superior in this invention, even whenthe amount of organic substance in the mixture of inorganic and organicmaterials as well as the coating amount is large, there is no need toreduce the coating amount at all to insure the welding characteristic bysacrificing the punching characteristic as in the conventional method,and the highest punching characteristics can be obtained without losingthe excellent welding characteristics.

Both sides or one side of the steel surface as well as the coating filmmay be made rough. lt suffices to make the surface somewhat rougher whenone side is made rough than in the casewhen both sides are made rough.It is desirous to contact the rough surface with'the smooth surface inpiling the punched steel sheets and strips when one side is made rough.

To make the steel surface rough, such methods as to pass through a rollhaving a rough surface, various etching methods and a method by means ofa scrubbing roller may be applicable.

As for the method of making the surface of coating film rough, forinstance, the method of treating the unhardened coating film by a rollerhaving a roughened surface during baking after an organic coating filmis applied uniformly, the method of forming a coating film havingstriped ditches on the surface of the steel sheet and strip by using acoating roller having ditches and then cutting barred ditches on theunhardened coating film by a steel roller having ditches during baking,and the method of applying a treating solution containing organicparticles with a particle size of greater than 2;; may be used.

As a particle to give roughness on the surface of organic film or a filmcomprising inorganic and organic materials, bakelite, melamine resin andthe like having a particle size greater than 2p. may be used.

The form of the organic coating film in this invention is as follows.

The first form is obtained by applying an organic coating film directlyon the steel sheet and strip, the second is obtained by making thecoating film a double layer by applying an organic coating film on thesurface of the steel sheet and strip which is coated previously with oneor more of a phosphoric acid type or chromic acid type coating material,and the third is to use a mixture of one or more of a phosphoric acidtype, or chromic acid type, coating material with an organic resin toobtain a coating film containing organic material.

To apply such a coating film, common methods such as the use of a rolleror a spray, coating by pouring, electrolysis and electro-deposition canbe adopted. The coating film is dried or baked finally by a hot blast orat 200 700C.

As the welding characteristic is superior in this invention, the coatingamount may be increased as compared with the amount of organic materialin the conventional method. The range of the coating amount is 0.5 l0g/mAs an organic coating film in this invention, a substance having polargroups, such as, calcium lignin sulfonate, polyvinyl alcohol, anhydrousmaleic acid resin, aminoacid resin and its denatured products, phenolresin and its denatured products, acrylic acid resin and its copolymers,vinyl acetate and its copolymers, alkyd resin, vinyl chloride and itscopolymers, polyvinyl acetal, epoxy resin and its denatured products anda mixture thereof, may be used.

The coating film containing one or more of a phosphoric acid type andchromic acid type material in this invention corresponds to theconventional inorganic type coating film. As a phosphoric acid typematerial, for instance, phosphate of calcium, magnesium, aluminium andzinc; oxide, hydroxide and carbonate of a divalent or tervalent metal,such as, calcium, magnesium, aluminium and zinc dissolved in phosphoricacid; and a mixture thereof are included. One or more of titanium oxide,colloidal silica, colloidal alumina, boric acid and the like may beadded thereto.

As a chromic acid type material, bichromate of calcium, magnesium andzinc; oxide, hydroxide and car-' bonate of divalent metal, such as,calcium, magnesium and zinc dissolved in an aqueous solution ofanhydrous chromic acid; and a mixture thereof are included. One or moreof titanium oxide, colloidal silica, colloidal alumina, boric acid andorganic reducing agent may be added thereto.

As an organic resin to be mixed with the inorganic film material, watersoluble-or emulsion type acrylic I acid resin and its copolymers, vinylacetate resin and its copolymers, butadiene styrene copolymer, aminoacidresin, alkyd resin, phenol resin, anhydrous maleic acid copolymer, epoxyresin and its denatured products, and a mixture thereof may be applied.

Some examples of the present invention will be set forth in thefollowing. Example 1 An electrical steel sheet (containing 0.7 percentof Si, 980mm width) was rolled by a rolling mill having a rough surfaceto obtain a steel strip of 0.5mm thickness and with a surface roughnessof 35 Hr.m.s.p.inch.

Said steel strip was coated with the treating solution I by a roller andbaked at 500C for 20 seconds. The coating amount was 6.5g/m

Steel strips having said coating film were piled and TIG welded. Evenunder a high welding speed of IOOcm/min. with an electric current of 120A, fine beads were obtained without the formation of blowholes.Separately, said steel strip was punched by a steel die (with aclearance of 6 percent), and 1,750,000 punchings were possible until theheight of .burr reached 50;!

As a comparison, a steel strip with the same quality as above and havinga usual surface roughness (7 I-Ir.m.s.p.inch) was coated with thetreating solution 1 by a roller. The coating amount was 6.4g/m

In the welding test of this steel strip under a welding speed of20cm/min., blowholes were formed on about a half of the beads. Under awelding speed of 10cm] min., the product was useable although someformation of blowhole was observed. By using a steel die, 1,800,000punchings were made until the height of burr reached 501.1,.

Treating solution I Calcium lignin sulfonate 30kg Polyvinyl alcohol 30kgPolyacrylic acid 2kg Water 300kg Example 2 An electrical steel sheet(containing 0.3 percent of Si, 1000mm width) was rolled by controllingthe rolling mill to obtain steel strips with varying surface roughnessof 5, 7, I3, 20, 25, 30, 40, 55, and I60 I-Ir.m.s.p.inch.

Each of the strips was coated with the treating solution 2 and baked at400C for 60 seconds. The coating amount was, respectively, 2.5, 2.4,2.4, 2.5, 2.5, 2.5, 2.5, 2.4, 2.6 and 2.5g/m

These steel strips were piled, and welded under the conditions of awelding electric current of A, screwing pressure of lOOkg/cm and varyingwelding velocity of 10 l00cm/min. The results were as shown in FIG.2(a). It is obvious from the results that, when the surface roughness isgreater than 20 I-Ir.m.s.p.inch, and particularly greater than 25Hr.m.s.p.inch, a quite satisfactory result can be obtained even underhigh welding speed.

In FIG. 4 (a), (b), (c), (d), (e) and (f), photographs of the weldedpart obtained with varying welding velocity for the samples having arough surface of 40 Hr.m.s.p.inch as well as a smooth surface are shown.

In the punching test for the samples with the surface roughness of 5I-Ir.m.s.p.inch and 40 Hr.m.s.;.tinch by using a steel die (clearance 7percent), 2,500,000 punchings and 2,650,000 punchings, respectively,were possible until the height of burr reached 50p" The punchingcharacteristic was quite excellent as compared with the case of a commoninorganic type insulating film.

An electrical steel sheet (rimmed steel, 970mm width) was rolled by arolling mill having a rough surface to obtain steel strips of 0.5mmthickness and with varying surface roughness as in Example 2. Thesesteel strips were coated with the treating solution 3, baked Treatingsolution 4 l.5% melamine resin mixed solution Other characteristics ofthe coating film in Examples 2 and 3 are shown in Table I. It is clearfrom the table that the insulating and anticorrosive characteristics ofthe inventive coating film is similar to or somewhat superior t theinorganic type coating film for smooth surface material, and theadhesive property by fusion of the inventive coating film is superior tothat of the smooth surface material.

1.5% alkyd resin TABLE l.-Characteristics of the film Example 2 Example3 Conventional (film coninorganic film taining (double (chromic acidorganic layer zinc oxide type) material) film) Hr.m.s. 4 0 5 40 s 40(smooth) (smooth) (smooth) Resistance max. 150.2 105.0 l2l.0 98.5 45.55.2 (JlS 2nd min. 92.0 55.5 98.5 45.5 35.5 l.'2 method) I mean l0l.065.0 I l 1.0 55.5 42.0 3.5

Kdhcs iVe 2 w property l0 l0 l0 I0 30 I0 Corrosion no rust spot no rustspot spot rust for-, resistance formarust formarust rust mation on tionformation formaformatotal tion tion tion surface Pin holes none nonenone none none numerous Adhesive property after annealing o o o 750C X 2hrs. in 100% N,

Coating ..i coat amount g/m 2.5 2.5 1.5 l.5 2.2 L5

' MW upper coat 4 i at 400C for 50 min.,'asase'n coated witht'reatlngso-"Elisabet lution 4 and baked again at 400C for min. to obtain a doublelayer coating film. The coating amount of under coat was 1.5g/m, andthat of the upper coat was 2.0 2.0, 2.1, 2.3, 2.1, 2.2, 2.0 and 2.2g/mrespectively.

These steel strips were piled and TIG welded under the conditions of awelding electric current of 120 A, a screwing pressure of l00kg/cm andvarying welding velocity of IO l00cm/min. The results were as shown inFIG. 2(b).

It is obvious from the results that, when the surface Treating solution3 Water l00kg Anhydrous chromic acid kg Calcium hydroxide 3kg Boric acid2kg Triethanolamine 2kg An electrical steel sheet (containing 0.5percent of Si, 980mm width) was rolled by a roller whose under roll wasrough to obtain steel strips of 0.5mm thickness. I

The surface roughness of the steel strip was: upper side 5 Hr.m.s.p,inchand under side 60 Hr.m.s.p.inch. Said steel strips were coated with thetreating solution 5 bya rubber roller and baked at 500C for 10 sec-Treating solution 5 Water l00kg Anhydrous chromic acid 20kg Calciumhydroxide 7kg Glycerine lkg Vinyl acetate acrylic acid copolymer 10kgemulsion solution) Example Electrical steel strips (containing 0.7percent of Si, 970mm width and having a surface roughness of 7Hr.m.s.;tinch) were coated with the the treating solution 1 (as inExample 1) by a rubber roller. During baking at 500C for 20 seconds,said steel strips were passed through a steel roller having a roughsurface. The coated amount was 6.5g/m and the roughness of the finishedsurface was 4.5 Ll-1 Steel strips having said coating were piled and T16welded. Even under a high welding speed of l00cm.min. with an electriccurrent of 120 A, fine beads were obtained without the formation ofblowholes. Separately, said steel strips were punched by a steel die(with a clearance of 6 percent), and 1,950,000 punchings were possibleuntil the height of burr reached 50p As a comparison, steel strips withthe same quality as above were coated with treating solution 1 by arubber roller. After baking under the usual conditions, the coatingamount was 6.4g/m and the surface roughness was less than 1 pH,,,,,

In the welding test of this steel strip under a welding speed of25cm/min., blowholes were formed on about a half of the beads. Under awelding speed of l0cm/min., the product was useable although someformation of blowholes was observed. By using a steel die, 1,800,000punchings were made until the height of burr reached 50 Example 6Electrical steel strips (containing 0.3 percent of Si, 1000mm width andhaving a surface roughness 7 Hr.m.s.;Linch) were coated with treatingsolution 2 (as in Example 2) by a rubber roller. During baking at 400Cfor 60 seconds, said steel strips were passed through a steel rollerhaving a rough surface. The surface roughness of the coating film was3.5 #PL and the coating amount was 3.2g/m

When said steel strips were piled and welded under the conditions of awelding electric current of 120 A, a screwing pressure lOOkg/cm and awelding speed l00cm/min., fine beads without no blowholes were obtained.

As a comparison, the same steel strips as above were treated with thetreating solution in the usual manner. The surface roughness was 0.6 pHand the coating amount was 3.1g/m.

When said steel strips were welded under the conditions of welding of anelectric current of 120 A, a screwing pressure of IOOkg/cm and a weldingspeed of 20cm/min., blowholes were formed on about a half of the beads.

1n the punching test of the inventive material steel strips in thisexample by using a steel die (clearance 7 percent), 2.650,000 punchingswere possible until the height of burr reached 50 ;1., showing that theresult is quite excellent as compared with the steel strip having aconventional inorganic type coating film.

Example 7 Electrical steep strips (rimmed steel, 970mm width with asurface roughness of 7 'Hr.m.s.p.inch) were coated with the treatingsolution 3 (as in Example 3), baked at 400C for 50 seconds, and thencoated with the treating solution 4 (as in Example 3). During baking at400C for 10 seconds, these steel strips were passed through a steelroller having a roughened surface to give surface roughnesses in of thefinal film of 2, 3, 4 and SuH The coating amount of the under coat wasLSg/m, and that of the upper coat was 2.9, 3.3 and 3.2g/m respectively.

These steel strips were piled and T16 welded under the conditions of anelectric current of A, a screwing pressure of l00kg/cm and a varyingwelding velocity of 10 l00cm/min. The results are as shown in FIG. 4. Inthe figure, the results with the surface roughness of the final film of0.5ul-l (3.0g/m and luH (3.1 g/m are also given as a comparison.

It is obvious that, when the surface roughness of the final film isgreater than 3p.H,,,,, an excellent result can be obtained under aremarkably high welding speed.

In the punching test of the samples with the surface roughness of 0.5and 40 ,uH by using a steel die, 1,950,000 and 2,100,000 punchings werepossible until the height of burr reached 50p" Example 8 Electricalsteel strips (containing 0.5 percent of Si, 980mm width and having asurface roughness 7 Hr.m.s.p.inch) were coated with treating solution 6by a rubber roller. During baking at 500C for 10 seconds, these steelstrips were passed through a steel roller whose upper roll was rough.The surface roughness of the one side of the coating film was ul-l andthat of the other side was 0.5;Ll-l The coating amount in total was6.4g/m ln punching them to obtain a motor core (85mm in diameter),2,300,000 punchings were possible until the height of burr reached 50;!"ln MlG welding of the strip after piling under the conditions of anelectric current of A, a screwing pressure of 45kg/cm and a weldingspeed of l00cm/min., the welding could smoothly be carried out withoutthe formation of blowholes.

Treating solution 6 l00kg lOkg 5kg Water Polyvinyl alcoholMclamine-alkyd resin roughness larger than 20 Hr.m.s.p.inch and havingan organic type coating film thereon selected from the group consistingof calcium lignin vsulfonate, polyvinyl alcohol, anhydrous maelic acidresin,aminoacid resin, phenol resin, acrylic acid resin or itscopolymers, vinyl acetate or its copolymers, alkyd resins, vinylchloride or its copolymers, polyvinyl acetal, epoxy resins, and mixturesthereof.

2. Electrical steel sheets and strips according to claim 1 which furthercomprises a coating film composed of one or more materials selected fromthe group consisting of phosphoric acid, and chromic acid and saltsthereof applied as an under coat for the organic type coating film.

3. Electrical steel sheets and strips having excellent punching andwelding characteristics for the production of a laminated iron corewhich comprise an electrical steel sheet or strip substrate having asurface rougher than 20 Hr.m.s.p.inch and having a coating film thereoncomposed of a mixture of one or more materials selected from the groupconsisting of phosphoric acid type and chrornicacid and salts thereofand an organic resin selected from the group consisting of calciumlignin sulfonate, polyvinyl alcohol, anhydrous maleic acid resin,aminoacid resin, phenol resin, acrylic

2. Electrical steel sheets and strips according to claim 1 which furthercomprises a coating film composed of one or more materials selected fromthe group consisting of phosphoric acid, and chromic acid and saltsthereof applied as an under coat for the organic type coating film. 3.Electrical steel sheets and strips having excellent punching and weldingcharacteristics for the production of a laminated iron core whichcomprise an electrical steel sheet or strip substrate having a surfacerougher than 20 Hr.m.s. Mu inch and having a coating film thereoncomposed of a mixture of one or more materials selected from the groupconsisting of phosphoric acid type and chromic acid and salts thereofand an organic resin selected from the group consisting of calciumlignin sulfonate, polyvinyl alcohol, anhydrous maleic acid resin,aminoacid resin, phenol resin, acrylic acid resin or its copolymers,vinyl acetate or its copolymers, alkyd resins, vinyl chloride or itscopolymers, polyvinyl acetal, epoxy resins, and mixtures thereof.